1. Field of the Invention
This invention relates to a discharge valve for a rotary refrigerant compressor.
2. Description of the Prior Art
FIGS. 1 through 4 illustrate a rotary compressor for a refrigerator as disclosed in Japanese Laid-Open Utility Model Publication No. 57174773, wherein a closed housing 1 contains a motor 2 and a compressor unit 3 comprising a cylinder 4, a crankshaft 5, a rolling piston 6, a radially slidable vane (not shown), and bearing end plates 7a, 7b closing the opposite ends of the cylinder to define a compression chamber A and support the crankshaft. The end plate 7a has a port 8 defined therein for discharging the refrigerant from the compression chamber A into the space within the housing. A valve plate 9 mounted on the end plate 7a has a free end 9a for opening and closing the discharge port 8. A leaf spring 10 is superposed on and fixed to the valve plate, and has a free end 10a for biasing the free end 9a of the valve plate into a closed position. A valve holder 11 is fastened by a bolt 12 to fix the opposite ends of the valve plate 9 and the leaf spring 10 to the bearing end plate 7a as shown in FIG. 3. The leaf spring has an intermediate bend at 10b for establishing its biasing force.
In operation, when the motor 2 is energized the crankshaft 5 is driven thereby to rotate the eccentrically mounted piston 6 and compress the refrigerant gas in the cylinder 4 as the volume of the chamber A varies. When the internal pressure in the compression chamber exceeds the sum of the pressure in the closed housing 1 and the biasing force of the leaf spring 10, the free ends of the valve plate 9 and the leaf spring flex upwardly to open the discharge port 8 and allow the compressed refrigerant gas to discharge into the housing.
By varying the thickness and/or shape of the leaf spring 10 with respect to the valve plate 9, the natural frequencies of the leaf spring and the valve plate are varied to reduce noises due to frictional damping forces generated between their contacting surfaces.
With the aforesaid construction of the conventional refrigerant discharge valve, the timing of the opening of the refrigerant discharge port is delayed by an interval corresponding to the resistance imposed by the leaf spring. The pressure in the cylinder 4 is thus built up to a higher level than the internal pressure in the housing, resulting in a so-called "overshoot" which requires an extra amount of drive power and lowers the efficiency of the compressor.